1. Field of the Invention
The present invention relates to control apparatus for executing a current feedback control of adjusting a current flowing in an electric rotary machine to an instruction current value, in particular, relates to a control apparatus for an electric rotary machine for controlling an AC voltage supply device capable of supplying an AC voltage to terminals of the electric rotary machine.
2. Description of the Related Art
There is a conventional known method of executing a current feedback control for executing a current feedback control of a current flowing in an electric rotary machine such as an electric motor and an alternating current (AC) synchronous machine. The current feedback control adjusts current components of a current of the AC synchronous machine flowing in a d-q coordinate system to current instruction values. Because such a known current feedback control method can adjust a direct current (DC) as a controlled variable, this allows a circuit designer to have an easy work of designing the current feedback control device in a control apparatus used for an electric rotary machine.
In order to have a DC current in a direct-Quadrature (dq) coordinate system when an electric motor has a constant torque, it is necessary to express an inductance, an interlinkage flux, etc. of the electric motor by using an exact sine function. In a case in which an inductance, etc. of an actual electric motor is expressed by a value which is shifted from an exact sine function (for example, which contains a higher harmonic wave), the electric motor has an increased torque ripple when components of a current in the d-q coordinate system are adjusted to corresponding instruction values.
In order to solve the above problem, there has been proposed a conventional technique, for example, Japanese patent No. 3852289, which adjusts components of a current in the dq coordinate system to values obtained by adding higher harmonic instruction values and DC instruction values. In more detail, the conventional technique executes:
the dq current feedback control which controls voltage instruction values in the dq coordinate system in order to adjust current components in the dq coordinate system of a current flowing in the electric motor; and
the higher harmonic dq axis feedback control which executes a coordinate transformation of higher harmonic components of a current flowing in the electric motor to DC components, and operates dq axis instruction values in order to adjust the transformed DC components to higher harmonic instruction values.
However, because the conventional technique previously described executes the dq feedback control for adjusting components of the current which flows in an electric motor to DC current instruction values, the components of a fundamental current and the higher harmonic current components of the current which flows in the electric motor into instruction values of the fundamental wave (DC instruction values in the dq coordinate system). As a result, there is a possibility of being it difficult to obtain convergence to the current instruction values because the interference occurs between the dq axis current feedback control and the higher harmonic dq axis current feedback control.